Rigid Body Sim: INTENTIONALLY breaking a chain, falling naturally...kinda
I think to have finally found what is causing that behaviour: you set a X+Y rotation lock on most chain rings...

Eg: the first one from top has free movement:



While most chain rings have X and Y rotation locked, as you can also see from the rotation manipulator:



To correct, select all chain rings, then - keeping ALT pressed - you toggle X and Y rotation locks for all selected objects. 

In this way your rigid body simulation should work better...